Amorphous BCN was prepared by ball milling the mixture of graphite and hexagonal BN for 120h, and then annealed for 45 min. at 1600K under 4.5GPa. The XRD，TEM and Raman scattering measurement indicated that the as-prepared sample consists of hexagonal phase Ⅰ with lattice constants a1=0.2551nm and c1=0.6716nm and hexagonal phase Ⅱ with lattice constants a2=1.2360nm and c2=0.8570nm, of which the hexagonal phase Ⅱ is an unknown phase of boron carbon nitride. Three characteristic Raman peaks located at 1279, 1368 and 1398cm-1 respectively, were observed in the Raman spectra recorded at room temperature. The temperature dependent Raman scattering spectra of the sample were taken at temperature ranging from 93 to 673K.The measuring results indicate that the hexagonal phase of Ⅰ mainly exist in the sample at 93K and hexagonal phase of Ⅰ convert to hexagonal phase of Ⅱ completely when at above 473K.The phase transition from the hexagonal phase of Ⅰ to Ⅱ occurs with increasing temperature, vice versa. The mechanism of the phase transition is discussed in the present work.